1. Field of the Invention
The present general inventive concept relates generally to a method to produce a transfer roller used in an image forming apparatus and the transfer roller. More particularly, the present general inventive concept relates to a method to produce a conductive transfer roller by passing through a continuous mobile oven foaming device. The produced conductive transfer roller is applicable to image forming apparatuses using electro photography, such as printers, copiers, and fax machines.
2. Description of the Related Art
FIG. 1 illustrates a conventional image forming apparatus 1. The image forming apparatus 1 includes a photoconductive member (a photoconductive drum 8), a charging means 4, an exposing means (not illustrated), a toner supply means 3 to supply toner 6, and a developing means 2 to form a transferable image from image data. A toner image is fused on a surface of a transfer medium (for example, a printing medium) to form a permanent image.
Typically, a conventional rotating contact transfer roller 5 is widely used as a means to transfer the toner image from the photoconductive drum 8. The conventional rotating contact transfer roller 5 can not only simplify the delivery path of the transfer medium but also stabilize the transfer medium delivery. The conventional transfer roller 5 is disposed in contact with the photoconductive drum 8. A nip part of the transfer medium and a transfer point are formed in the contact surface between the conventional transfer roller 5 and the photoconductive drum 8. When a voltage is applied to the conventional transfer roller 5, the transfer medium is delivered through the transfer point and the toner image on the photoconductive drum 8 is electrostatically transferred onto the transfer medium. To charge the photoconductive drum 8 and the transfer medium, the conventional transfer roller 5 should be electrically conductive.
As discussed above, to make the toners of the photoconductive drum 8 achieve enough transferring effect, the contact surface between the photoconductive drum 8 and the conventional transfer roller 5 should be kept constant. For doing so, the conventional transfer rollers currently in use are formed of a rubbery elastic roller. Mostly, the rubbery material includes ethylene propylene (EPDM) rubber, acrylonitrile butadiene (NBR) rubber, silicon, and urethane rubber. Preferably, the rubbery material has low hardness to enhance close contact with the drum 8.
The conventional transfer roller 5 is classified as an ionic conductive type and an electron conductive type. The electron conductive type features the stable resistance according to its environment. However, it is quite hard to regulate the amount of carbon to adjust the resistance in the production. Since a shaft (not illustrated) of the conventional transfer roller 5 is pressed with an elastic layer, the elastic layer is likely to deform. The non-uniform electric resistance makes it hard to acquire the uniform electronic conductivity. The ionic conductive type does not suffer the non-uniform resistance even when the elastic layer is deformed. However, its severe resistance change according to the environment requires high voltage. The photoconductive drum 8 may be contaminated because of the leakage of a charging control material added in the production of the conventional transfer roller 5.
A conventional transfer roller producing method produces a rubber composite which mixes a polymer with a vulcanizing agent, a blowing agent, and a filler, in the form of an unvulcanized tube using a mold or an extruder. Next, the unvulcanized tube is vulcanized and blown with heated air to produce a foaming rubber tube. The foaming rubber tube is pressed to the shaft spread with adhesives, and the intended external diameter is ground.
The vulcanized foaming method for articles extruded from an unvulcanized tube includes a mold forming vulcanization using a general press, a direct/indirect vulcanization using a vulcanizing pipe, and a hot wind vulcanization. However, it is hard to transfer the uniform heat to the rubber material and to acquire the uniform foam in the mold forming vulcanization or the hot wind vulcanization. Thus, a vapor vulcanization using the vulcanizing pipe is generally used. However, the vapor vulcanization is a batch production method. Since the vapor vulcanization cuts the rubber tube produced from the extruder at a certain part and then vulcanizes and foams the cut rubber tube, the uniform heat is hardly transferred in the longitudinal direction of the rubber tube and a foam line may be formed in the longitudinal direction.